- Alzheimer s disease (AD) is a brain disease that impairs memory, cognitive abilities and the ability to function independently. It is the most common cause of dementia in older people. It is caused by abnormal proteins in the brain that affect how neurons communicate with each other. Researchers are looking for drugs that can slow down the disease or treat its symptoms. One drug, called bisnorcymserine (BNC), may help improve brain function and symptoms in people with AD. BNC is designed to block a chemical that affects how neurons communicate with each other. Researchers want to see how BNC works in healthy older volunteers.